1. Field of the Invention
This invention pertains to the storage or backup of data using magnetic tape drives, and particularly to the cleaning of transducing elements utilized in magnetic tape drives.
2. Related Art and Other Considerations
In magnetic recording on tape using a magnetic tape drive, relative motion between a head unit (typically with both a write element and a read element) and the tape causes a plurality of tracks of information to be transduced with respect to the tape. The magnetic tape is typically housed in a cartridge which is loaded into the tape drive. The tape extends between a cartridge supply reel and a cartridge take-up reel. The tape drive typically has a supply reel motor for rotating the cartridge supply reel and a take-up reel motor for rotating the cartridge take-up reel.
After the cartridge is loaded into the tape drive, the tape is extracted or loaded by mechanisms in the drive so that a segment of the tape is pulled from the cartridge and into a tape path that travels proximate the head unit. In some tape drives the extraction mechanisms take the form of tape guides which are mounted on trolleys. During the extraction operation, trolley motors move the trolleys along a predefined trolley path, so that the tape guides which surmount the trolleys displace the tape into the tape path as the trolleys travel along the trolley path. When the trolleys reach the full extent of travel along the trolley path, the tape is proximate the head unit. Thereafter the tape can be transported past the head unit, e.g., by activation of a capstan and/or the supply reel and take-up reel motors, depending upon the particular type of transport mechanisms employed. A capstanless tape drive, particularly a tape drive which utilizes helical scan recording, is shown in U.S. Pat. No. 5,602,694 for CAPSTANLESS HELICAL DRIVE SYSTEM, which is incorporated herein by reference.
As the tape is transported past the head unit, information can be transduced to or from the tape by the tape drive in recording and reading operations, respectively. When the recording and/or reading operations are concluded, and before the cartridge can be unloaded from the drive, the tape must be retracted for return to the interior of the cartridge. Tape retraction is essentially the reverse of the tape extraction procedure described above.
The head unit head unit which includes both one or more write elements and one or more read elements can take the form of a drum around which the tape is partially wrapped. The read and write elements are positioned proximate or on a circumferential surface of the drum. Such a drum with read and write elements is also called a "scanner."
Over time the scanner with its write and read elements can acquire dust or other contaminants. For example, the tape media can introduce the contaminants into the drive or contribute to the collection of debris on the read and write elements as the tape media deteriorates. The presence of such contaminants proximate the write and read elements can degrade the signal recorded on or read from tape media, thereby spawning errors.
Some magnetic tape drives incorporate cleaning mechanisms which endeavor to clean the scanner by removal of contaminants. One type of cleaning mechanism is a roller or wheel which is moved into contact with the periphery of the scanner in order to wipe the write and read elements on the scanner. Examples of cleaning mechanisms are illustrated in the following United States Patents: U.S. Pat. No. 5,473,493 to Kusui; U.S. Pat. No. 5,182,691 to Mimasu et al.; U.S. Pat. No. 5,170,304 to Katohno et al.; U.S. Pat. No. 5,523,913 to Kim; U.S. Pat. No. 3,964,104 to Herron et al.; U.S. Pat. 5,386,333 to Kang et al.; U.S. Pat. No. 5,341,257 to Dienbauer; U.S. Pat. 5,335,128 to Morinaka; and U.S. Pat. No. 3,731,289 to Bajgert et al.
In some instances the cleaning roller or wheel is fabricated from a foam or other material which is sufficiently pliant enough so as to not cause concern about the duration of contact of the cleaning wheel with the scanner. Cleaning wheels generally have superior durability, however, when formed from a less pliant material. Yet usage of less plaint materials for cleaning wheels have introduced complications as explained below.
In a prior art tape drive such as that shown in U.S. Pat. No. 5,602,694, contact of the cleaning wheel with the scanner is coordinated with movement of the tape extraction trolleys. In particular, a cam is attached to geared output of a motor for a trolley drive system, and in response to the cam the cleaning wheel moves into or out of contact with the scanner. To engage the cleaning wheel with the scanner, the trolleys were moved a fixed distance away from a trolley docked position. This fixed distance was calculated to guarantee, given the material and process variations between drives, that the cleaning wheel would engage the scanner in all drives. Because the cleaning wheels were made of a soft material, it did not matter that the cleaning wheels on some drives would touch the scanner for longer periods of time than cleaning wheels on other drives.
The advent of firmer cleaning wheel materials such as cloth or Vilene afforded greater durability. However, these firmer materials do not compress significantly when pressed against the scanner. Given the variation from drive to drive regarding time of contact of the cleaning wheel with the scanner, excessive contact of a firm cleaning wheel with a scanner causes greater wear to both the cleaning wheel and the write and read elements (e.g., the write and read heads).
What is needed, therefore, and an object of the present invention, is a technique for precisely controlling the contact time of a cleaning wheel with a scanner in a magnetic tape drive.